1. Field of the Invention
The present invention relates to a construction machine such as a digger, in which an exhaust structure is provided to discharge a lower airflow that flows under an engine in an engine room.
2. Background Art
The background art will now be described, using a digger as an example of a construction machine.
As shown in FIG. 8, a digger includes a lower propelling body 1, an upper slewing body 2 that is carried on the lower propelling body 1 to be free to slew, various pieces of equipment and various devices carried on an upper frame 3 serving as a base of the upper slewing body 2, and a work attachment (also referred to as a digging attachment) 5 attached to a front portion of the upper frame 3. The various pieces of equipment carried on the upper frame 3 include a cabin 4. In FIG. 8, CW denotes a counterweight attached to a rear end portion of the upper frame 3.
Note that in this specification, a position of the cabin 4 is set as a left side front portion, and “front-rear” and “left-right” directions are based on the position of the cabin 4.
Further, to simplify the drawings and the description, detailed illustration and description of respective portions of the upper frame, which are not directly related to the present invention, have been omitted.
An engine room 7 housing an engine 6 is provided in a rear portion of the upper frame 3.
FIG. 9 is a schematic sectional view showing an arrangement of devices in the engine room 7 from a back surface side.
As shown in FIG. 9, the engine room 7 is a space that is long in the left-right direction and surrounded by a base plate 8 of the upper frame 3, an engine guard member 9 such as a panel material, the counterweight CW shown in FIG. 8, and so on. A bottom surface of the engine room 7 is formed by the base plate 8 of the upper frame 3. The engine 6 is disposed in the engine room 7 via a mounting member, not shown in the drawing, so as to extend in the left-right direction.
Meanwhile, a left-right pair of vertical plates 10, 11 doubling as reinforcing members and attachment mounting members are provided in an intermediate portion, in a vehicle width direction, of the base plate 8 of the upper frame 3. The vertical plates 10, 11 are provided at an interval in the left-right direction so as to extend perpendicularly to the base plate 8 along substantially an entire length of the base plate 8 in the front-rear direction. The engine 6 is disposed above the vertical plates 10, 11.
As a result, a ventilation gap S through which air can pass is formed in the engine room 7 below the engine 6.
Further, a fan 12 and a heat exchanger 13 such as a radiator or an oil cooler are provided on one side of the engine 6, or more specifically a right side of the engine 6, while a hydraulic pump 14 is provided on an opposite side of the engine 6, or more specifically a left side of the engine 6. An intake port 15 is provided in the vicinity of a right end of an upper surface wall covering an upper surface of the engine room 7. When the fan 12 is rotated, outside air is taken into the engine room 7 through the intake port 15, and the intake air forms a cooling airflow that flows through the engine room 7 from the right side to the left side. The heat exchanger 13 and the engine 6 are cooled by this airflow.
Japanese Patent Application Publication No. 2005-186910 discloses a conventional technique for improving a discharge performance of a lower airflow, which forms a part of the aforesaid airflow that passes through the ventilation gap S, as shown by an arrow in FIG. 9. This conventional technique will now be described on the basis of FIG. 9.
In this conventional technique, a fire wall 17 is provided on the left side, or in other words the hydraulic pump 14 side, of the engine room 7. The fire wall 17 is provided to partition the engine 6 from the hydraulic pump 14. The fire wall 17 is provided to prevent mist-form oil that is leaked or scattered from the hydraulic pump 14 from falling onto the engine 6, or more accurately an exhaust system of the engine 6 including a muffler 16.
Further, an air passage forming member 18 is attached between a lower end of the fire wall 17 and the base plate 8 of the upper frame 3. The air passage forming member 18 is formed in an inverted L shape such that an upper portion thereof is disposed horizontally and a lower portion is disposed vertically. An air passage 19 that communicates with the ventilation gap S is formed by the air passage forming member 18, the left vertical plate 10, and the base plate 8 of the upper frame 3. Further, an exhaust chamber 20 is defined in a left side region of the engine room 7 by the air passage forming member 18 and the fire wall 17.
Furthermore, an air passage outlet 21 is formed to open in a vertical part of the air passage forming member 18. A lower portion exhaust port 22 is opened in a part of the base plate 8 of the upper frame 3 that forms a lower surface of the exhaust chamber 20. An upper portion exhaust port 23 is provided in a part of an upper surface wall of the engine guard member 9 that forms an upper surface of the exhaust chamber 20. The lower airflow passing through the ventilation gap S enters the exhaust chamber 20 through the air passage 19 and the air passage outlet 21, and is discharged to the outside through the two exhaust ports 22, 23.
With the configuration described above, the lower airflow is caused to flow smoothly on the exhaust side, thereby improving an air discharge performance.
Incidentally, in the conventional technique described above, the hydraulic pump 14 penetrates the fire wall 17 so as to infiltrate the exhaust chamber 20. Therefore, the hydraulic pump 14 can be seen clearly from the exterior of the exhaust chamber 20 through the two exhaust ports 22, 23, and as a result, pump noise cannot be blocked completely from the outside. Hence, an increase in pump noise leakage to the outside, including “direct sound” emitted directly to the exterior of the exhaust chamber 20 from the hydraulic pump 14, occurs.
Furthermore, in the conventional technique described above, when an attempt is made to reduce pump noise leakage using a sound absorbing material such as glass wool, a sufficient sound absorption effect cannot be obtained unless the sound absorbing material is provided over a wide range of the exhaust chamber 20, including the vicinity of the exhaust ports 22, 23.
Therefore, an amount of used sound absorbing material increases, leading to an increase in cost, and moreover, when the sound absorbing material is provided over a wide range of the exhaust side, devices disposed on the exhaust side, not shown in the drawings, cannot easily be installed due to limitations on sizes and positions of the devices.